The long-term goal of this project is to utilize newly available very high-speed optical coherence tomography (OCT) technology to guide surgical treatments of anterior eye diseases. Measuring aberrations in the optical surfaces of the cornea requires great precision. OCT is well known for its exquisite spatial resolution, but until recently it has not had sufficient speed to overcome the inherent biological motion of the eye and capture the shape of the cornea. The development of Fourier-domain (FD) OCT technology has made the requisite speed possible. The specific aims are: (1) To develop a very high-speed anterior segment OCT instrument. An FD-OCT system capable of 26,000 axial scans/second and 5-5m resolution has been tested. Preliminary data show that it is able to map corneal thickness with a precision of 1-5m root-mean-square and measure corneal power with a precision of 0.2 diopters. Motion correction algorithms will be developed to further improve the precision. (2) To develop OCT-guided corneal laser surgery for the treatment of irregular and opacified corneas. Although wavefront sensing and Placido-ring topography have been used to guide laser corneal surgeries, they are often unable to make valid measurements of irregular corneas. Our preliminary results showed that OCT can reliably make measurements in these diseased corneas that are most in need of surgical remedy. Corneal thickness or topography maps obtained by the OCT system will be used to program the depth of femtosecond laser corneal dissection and excimer laser ablation. OCT-guided femtosecond laser lamellar keratoplasty and excimer laser phototherapeutic keratectomy (PTK) will be tested in rabbit studies. Patients with corneal scar, ectasia, dystrophy, or irregular astigmatism following corneal surgery will be scanned, and laser surgery will be simulated by computer to evaluate the visual outcome. The simulation will take into account measurement variability, laser delivery error, healing effects, and visual optics. These tests will prepare for future human trials. (3) To develop an OCT-based intraocular lens (IOL) power formula. IOL power selection is difficult in patients who have had previous laser vision correction, often resulting in significant near- or far-sightedness after the cataract surgery. Laser ablation alters the natural relationship between the front and back corneal surfaces, causing error in conventional keratometry and IOL calculation. This increasingly common problem could be solved by measuring both anterior and posterior corneal powers with OCT. The OCT-based IOL formula will be tested in a clinical trial. The aim of this project is to develop methods for imaging the cornea with a very high-speed and high-resolution optical coherence tomography (OCT) system that will precisely measure corneal thickness and shape and use this information to guide eye surgery. Patients with irregularly shaped or scarred corneas could have their vision restored by reshaping the corneas with a procedure that combines the precision of OCT and lasers instead of traditional corneal transplantation, which is associated with slow visual recovery and risks of transplant rejection. Cataract surgery in patients with previous laser vision correction often leads to significant near- or far-sightedness, a problem that could be resolved by using a more accurate intraocular lens power selection formula based on the measurement of corneal refractive power with OCT.